User interface widgets that are part of a web browser's content (such as web forms) are actually handled by a separate toolbox --- rather than XP Toolkit --- and should be assigned to Layout: Form Controls.

We need to change the nsIController APIs for embedding. The main changes are:
1. Addition of a method for getting command state
2. Adding a commandParams parameter to doCommand
3. Conversion to use DOMString

The DOMString parts of these changes were checked in for bug 74143. The other
part of these changes is the addition of a command params string argument, which
will change to an nsICommandParams (see bug 74927).
I'm going to make an nsIController2 or somesuch, rather than messing with
nsIController, and I'll make a new bug for that (see the dependencies on bug
66305), so closing this one.